A camshaft formed of an inner shaft and an outer tube both of which rotate with respective groups of cams, is known and is termed herein a single cam phaser (SCP) camshaft. GB 2 369 175 also teaches that a vane type phaser may be fitted to an SCP camshaft in order to control the timing of the inner shaft or the outer tube relative to the crankshaft.
In GB 2 369 175, and other prior art references such as EP 0 254 058 and US 2003/0154944, in which a phaser is mounted on the front end of an SCP camshaft, the phaser is held axially against the end of the camshaft by being bolted to a front end of the inner drive shaft. This results in radial drive loads from the timing chain or belt of the drive train being transmitted through the front bearing supporting the inner shaft in the outer tube.